Fat Mass & Fat-Free Mass Calculator
Split body weight into fat mass and fat-free mass in kilograms from a body-fat percentage.
Kilograms tell a clearer story than percentages: gaining muscle while keeping fat constant lowers BF% with zero fat lost, and percentage alone can't show which compartment changed. Tracking FM and FFM separately is how body-recomposition progress is actually measured.
Formula
For general information only — not medical or training advice. Estimates vary between individuals; consult a qualified professional before changing your exercise or nutrition routine.
Split body weight into fat mass and fat-free mass in kilograms from a body-fat percentage. The Fat Mass & Fat-Free Mass Calculator is a free, private fat mass tool — every result computes instantly in your browser with no sign-up and no data upload.
About Fat Mass & Fat-Free Mass Calculator
Kilograms tell a clearer story than percentages: gaining muscle while keeping fat constant lowers BF% with zero fat lost, and percentage alone can't show which compartment changed. It applies FM = weight × BF%; FFM = weight − FM. Use the Fat Mass & Fat-Free Mass Calculator to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Fat Mass & Fat-Free Mass Calculator
- 1Enter your details in the Fat Mass & Fat-Free Mass Calculator input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Fat Mass & Fat-Free Mass Calculator?
- ✓Instant fat mass result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (Wang Z et al., Am J Clin Nutr 1992 — the five-level model of body composition)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Fat Mass & Fat-Free Mass Calculator work?+
Kilograms tell a clearer story than percentages: gaining muscle while keeping fat constant lowers BF% with zero fat lost, and percentage alone can't show which compartment changed. The calculation uses the formula: FM = weight × BF%; FFM = weight − FM. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Fat Mass & Fat-Free Mass Calculator accurate, and what is it based on?+
The method is traceable to authoritative sources: Wang Z et al., Am J Clin Nutr 1992 — the five-level model of body composition. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Fat Mass & Fat-Free Mass Calculator free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is for general fitness information only, not medical or training advice. Consult a professional before changing your routine.
What can I use the Fat Mass & Fat-Free Mass Calculator for?+
It's commonly used for fat mass, fat free mass, ffm calculator. Split body weight into fat mass and fat-free mass in kilograms from a body-fat percentage.
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